|Season 4, Episode 43|
|Airdate:||December 10, 2004|
|Writer(s):|| Mo Willems|
|Storyboards by:|| Kim Arndt|
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| Next Mission|
Prevent Opposite Operative's Larceny
Summary: Numbuh 4's new pool is actually a portal to an alternate version of the KND Universe where their counterparts know as the DNK (Destructively Nefarious Kids) are evil. The kids do all the adults job's whereas the adults sit around and play video games. While swimming in the pool, Lizzie is captured by an evil opposite of herself, Eizzil Enived (Lizzie's name backwards), and Nigel follows the captor back to her home universe.
- Villain Debuts: Negative Numbuh 4
- Ally Debuts: Destructively Nefarious Kids and Little Traitor Dudes For Children's Defense
- Numbuh 4 house
- DNK Treehouse
- Sector V Treehouse
- In the credits, the pool now has sand in it, and Numbuh 4 sings a song about it.
- This episode is somewhat based off the Star Trek episode entitled "Mirror, Mirror", where the crew of the Enterprise encounter their own evil twins. The Evil Spock had a goatee like Negative Numbuh 4's, which denotes evil twin status.
- This episode is somewhat based on Batman: The Brave and the Bold 2-part episodes entitled "Deep Cover for Batman" and "Game Over for Owlman" where the DNK are based on the Injustice Syndicate and the LTDFCD are based on the Justice Underground.
- Everything is completely opposite of the real world, both of the organizations and the characters' personalities. For example, the DNK are evil, and the LTDFCD and Daddy are good. Their names also seem to be reversed in spelling (Lizzie's counterpart's name is Eizzil).
- This episode indirectly reveals that Numbuh 3 actually likes Numbuh 4. At one point in the episode, Anti-Numbuh 3 says to Numbuh 4 she does not like him. Since Anti-Numbuh 3 is the complete opposite of Numbuh 3, it indirectly means that Numbuh 3 likes Numbuh 4.
- Numbuh 4, finally but barely learns to swim in this episode, as he was still hesistant to swim in the following episode.
- When Negative Numbuh 4 is jumping off of the diving board to go to the positive world, it doesn't show Positive Numbuh 4 on the diving board when he was there less than 2 seconds before he jumped.
- We don't see exactly how Numbuh 4 defeated the Negative Sector V, but is worth noticing that they appear in worse shape than their positive counterparts, despite the latter being tortured with electricity.
- This is the last season and episode to air in 2004.
- If the little traitor dudes are good, that means that they may be DNK operatives meaning that they're truly evil.
- This is the second time where we see Numbuh 3 got captured and chained up, but among with the others in this episode. (Numbuh 1, Numbuh 2, Numbuh 5 and Lizzie).
- This episode foreshadows DCFDTL and Father's true origins in Operation: Z.E.R.O.:
- If you notice the alternate universe's acronyms, they are said to be traitors. The DCFDTL are also traitors.
- Daddy's looks is what Father's looks if he wasn't black.
- The Teen Ninjas (including Cree Lincoln and Chad Dickson) are implied to be good as well in the negative world (assuming that they're evil in the positive world).
- Goof: When Negative Numbuh 2 tells his joke about Negative Numbuh 4's goatee, Numbuh 2 can be seen laughing along with everyone else. However in the next scene, Numbuh 2 is clearly not amused by the joke.